rsync/incementral

[Ashley Aitken]

On 31/07/2007, at 12:41 AM, steve harley wrote:

> a can't find a single mention of hard links in the RxyncX docs ...

Sorry,  I haven't got time to search the docs.   Google get this:

<http://www.macosxhints.com/article.php?story=2006051913572885>

> i'm still not convinced the hard links approach works anyway, since  
> i had heard of the same failings Izidor mentioned;

We know hard links are simulated on HFS+.

As a result, they aren't as efficient (space and time) as real hard  
links on Unix.  And there may be some quirks.  However, I believe,  
generally speaking, they work ok.

> perhaps these failings don't matter if the backed up files are  
> never moved or changed; here's a detailed but dated description of  
> what can go wrong, along with some reference material:
>
> <http://rixstep.com/2/20040621,00.shtml>
> (the behavior i see in 10.4.9 is that Preview alerts the user on  
> Save that the document has been "renamed" when a hard link has been  
> made to it)

I am not sure what exactly caused that problem.  Maybe when a hard  
link is first set-up it requires some change to the original file's  
entry in HFS+.  Doing this while the file was open could cause  
problems (if the app, perhaps, didn't do the right thing).

> an alternative to consider is rdiff-backup, which doesn't rely on  
> hard links
>
> <http://www.nongnu.org/rdiff-backup/features.html>

I remember looking at that as well but I am not sure how it can  
provide complete incremental backups without using hard links (if  
complete backups are a requirement).

As I said, RsyncX (which is just a GUI wrapper around rsync) seemed  
to work fine for me - but I would watch out if you use recent  
filesystem features (like ACLs).

Cheers,
Ashley.